1. Field of the Invention
The present invention generally relates to a method of and apparatus for transmitting digital data, and more particularly, is directed to improvements in a digital data transmitting method by which 12-bit word sequence data constituting a digital video signal which represents video signal information are converted into serial data to be transmitted, and in a digital data transmitting apparatus used for putting the above-mentioned method into practice.
2. Description of the Prior Art
In the field of video signals, digitalization of video signals has been aimed for actualizing diversification in information to be transmitted, improvements in quality of images reproduced from the video signal and so on. For example, there has been proposed the High Definition Television (HDTV) system which uses a digital video signal composed of word sequence data representing video signal information.
The digital video signal under the HDTV system (hereinafter, referred to an HD signal) is formed into word sequence data in accordance with a standardized data formats in the form of Y and PB/PR signals or G, B and R signals. In the case of the Y and PB/PR signals, Y represents a luminance signal and PB/PR represent color difference signals. In the case of the G, B and R signals, G, B and R represent green, blue and red primary color signals, respectively.
The HD signal produced in the form of Y and PB/PR signals (hereinafter, referred to an HD signal of the Y and PB/PR type) contains a Y data sequence and a PB/PR data sequence, each of which forms, for example, 10-bit word sequence data composed of a sequence of 10-bit words, and which are combined in parallel with each other in frame be synchronized at every line period and every frame and line synchronism so as to form 20-bit word sequence data composed of a sequence of 10-bit word×2=20-bit words. Further, the HD signal produced in the form of G, B and R signals (hereinafter, referred to an HD signal of the G, B and R type) contains a G data sequence, a B data sequence and an R data sequence, each of which forms, for example, 10-bit word sequence data composed of a sequence of 10-bit words, and which are combined in parallel with one another in frame and line synchronism so as to form 30-bit word sequence data composed of a sequence of 10-bit word×3=30-bit words.
Although, under the current HDTV system, the HD signal of the Y and PB/PR type or the G, B and R type for interlaced scanning by which each frame picture is reproduced at a rate of 30 Hz or 30/1.001 Hz (hereinafter, the expression:30 Hz includes both of 30 Hz and 30/1.001 Hz) with first and second field pictures, is used for reproducing color pictures, there has been proposed, as an HDTV system for the next generation, another HDTV system in which an HD signal of the Y and PB/PR type or the G, B and R type for sequential scanning by which each frame picture is reproduced at a rate of 60 Hz or 60/1.001 Hz (hereinafter, the expression:60 Hz includes both of 60 Hz and 60/1.001 Hz) or 50 Hz without first and second field pictures. That is, the HD signal of the Y and PB/PR type or the G, B and R type for interlaced scanning has a frame rate of 60 Hz or 50 Hz. This HD signal of the Y and PB/PR type or the G, B and R type for sequential scanning which has the frame rate of 60 Hz or 50 Hz is usually called a progressive HD signal.
Digital data constituting the progressive HD signal having the frame rate of 60 Hz or 50 Hz have been standardized in data formats in accordance with SMPTE 274M which is one of a series of standards established by the Society of Motion Picture and Television Engineers (SMPTE) in the United States. In the data formats standardized in accordance with SMPTE 274M, 1920 active data samples per line, 1080 active lines per frame, the sampling frequency of 148.5 MHz or 148.5/1.001 MHz (hereinafter, the expression:148.5 MHz includes both of 148.5 MHz and 148.5/1.001 MHz), 8 or 10 bits for one word and so on are predetermined in addition to the frame rate of 60 Hz or 50 Hz. Then, parallel data interface is selected to be 8 bits×2=16 bits or 10 bits×2=20 bits for data of the Y and PB/PR type and 8 bits×3=24 bits or 10 bits×3=30 bits for data of the G, B and R type.
For such 8-bit or 10-bit digital data constituting the digital video signal as mentioned above, some forbidden codes which can not be used for representing any video signal information are predetermined. For example, the forbidden codes for 8-bit digital data are 00h and FFh (00 and FF are hexadecimal numbers and h indicates a hexadecimal number), that is, “0000 0000” and “1111 1111”, and the forbidden codes for 10-bit digital data are 000h˜003h and 3FCh˜3FFh (000, 003, 3FC and 3FF are hexadecimal numbers and h indicates a hexadecimal number), that is, “00 0000 0000”˜“00 0000 0011” and “11 1111 1100”˜“11 1111 1111”. Some of these forbidden codes, for example, 000h and 3FFh are used for constituting a pair of time reference code data SAV (Start of Active Video) and EAV (End of Active Video) provided just before and after a portion of the digital video signal corresponding to each video data period.
Generally, in the case of the digital video signal of the Y and PB/PR type, the sampling frequency of each of the PB data sequence and PR data sequence is selected to be a half of the sampling frequency of the Y data sequence. Hereinafter, as occasion demands, the digital video signal of the Y and PB/PR type will be indicated as a digital video signal of the 4:2:2 type. On the other hands, in the case of the digital video signal of the G, B and R type, the respective sampling frequencies of the G, B and R data sequences are the same as one another. Hereinafter, as occasion demands, the digital video signal of the G, B and R type will be indicated as a digital video signal of the 4:4:4 type.
Apart from the HD signal as described above, there has been also proposed a kind of progressive HD signal which is aimed for reproducing moving pictures of a cinefilm at twenty-four frames per second with so improved quality as to be substantially equal to that of images reproduced by means of the HDTV system and so-called a D-Cinema signal.
Although the D-Cinema signal is able to be obtained in the form of one of the progressive HD, the frame rate of which is selected to be, for example, 24 Hz or 24/1.001 Hz (hereinafter, the expression:24 Hz includes both of 24 Hz and 24/1.001 Hz) as mentioned above, the frame rate of the D-Cinema signal is selected to be not only 24 Hz but also a rate other than 24 Hz, for example, 25 Hz or 30 Hz. Then, the D-Cinema signal is also formed into word sequence data in the form of Y and PB/PR signals or G, B and R signals.
The D-Cinema signal produced in the form of Y and PB/PR signals (hereinafter, referred to a D-Cinema signal of the Y and PB/PR type) contains a Y data sequence and a PB/PR data sequence, each of which forms, for example, 10-bit word sequence data composed of a sequence of 10-bit words, and which are combined in parallel with each other in frame and line synchronism so as to form 20-bit word sequence data composed of a sequence of 10-bit×2=20-bit words. Further, the D-Cinema signal produced in the form of G, B and R signals (hereinafter, referred to a D-Cinema signal of the G, B and R type) contains a G data sequence, a B data sequence and an R data sequence, each of which forms, for example, 10-bit word sequence data composed of a sequence of 10-bit words, and which are combined in parallel with one another in frame and line synchronism so as to form 30-bit word sequence data composed of a sequence of 10-bit×3=30-bit words.
Differing from the HD signal, any forbidden code which can not be used for representing video signal information is not predetermined for the D-Cinema signal. This means that, in the case of the D-Cinema signal, for example, the 10-bit digital data 000h˜003h and 3FCh˜3FFh which are the forbidden codes for the HD signal can be used for representing video signal information.
Digital data constituting the digital video signal having the frame rate of 24 Hz, 25 Hz or 30 Hz have been standardized also in data formats in accordance with SMPTE 274M. In such data formats standardized in accordance with SMPTE 274M, 1920 active data samples per line, 1080 active lines per frame, the sampling frequency of 74.25 MHz or 74.25/1.001 MHz (hereinafter, the expression:74.25 MHz includes both of 74.25 MHz and 74.25/1.001 MHz), 8 or 10 bits for one word and so on are predetermined in addition to the frame rate of 24 Hz, 25 Hz or 30 Hz. Then, parallel data interface is selected to be 8 bits×2=16 bits or 10 bits×2=20 bits for data of the 4:2:2 type and 8 bits×3=24 bits or 10 bits×3=30 bits for data of the 4:4:4 type.
Under such a condition, it has come to be desired to produce the digital date constituting the HD signal or the D-Cinema signal with a sequence of words each made of more than 10 bits, for example, 12 bits, that is, a 12-bit word sequence.
In general, when the HD signal or the D-Cinema signal formed with, for example, 10-bit or 12-bit word sequences are transmitted through a data transmission path constituted with, for example, a single or a plurality of coaxial cables or optical fibers, it is desired that the word sequence data (parallel data) constituting the HD signal or the D-Cinema signal are converted into bit sequence data (serial data) to be subjected to serial transmission because the data transmission path can be simplified in structure. It has been standardized by the SMPTE that the HD signal of the 4:2:2 type formed with 10-bit word sequences is to be subjected to serial transmission in accordance with HD SDI (High Definition Serial Digital Interface) provided by SMPTE 292M which is one of the standards established by the SMPTE. Further, It has been also standardized by the SMPTE that the HD signal formed with 12-bit word sequences is to be subjected to serial transmission in accordance with Dual Link 292M Interface provided by SMPTE 372M which is one of the standards established by the SMPTE.
In the serial transmission in accordance with HD SDI provided by SMPTE 292M, the HD signal of the 4:2:2 type formed with 10-bit word sequences so as to contain the time reference code data SAV and EAV constituted with the forbidden codes is converted into digital bit sequence data having a data rate (bit rate) of, for example, 1.485/1.000 Gb/s or 1.485/1.001 Gb/s and then transmitted through a data transmission path. In the serial transmission in accordance with Dual Link 292M Interface provided by SMPTE 372M, the HD signal formed with 12-bit word sequences so as to contain the time reference code data SAV and EAV constituted with the forbidden codes is converted into bit sequences data of two channels each having a data rate (bit rate) of, for example, 1.485/1.000 Gb/s or 1.485/1.001 Gb/s or a multiplexed bit sequence data having a data rate (bit rate) of, for example, 2.970/1.000 Gb/s or 2.970/1.001 Gb/s, which is constituted with the bit sequence data of two channels each having the data rate (bit rate) of, for example, 1.485/1.000 Gb/s or 1.485/1.001 Gb/s multiplexed with each other, and then transmitted through a data transmission path.
Although the serial transmission of the HD signal of the 4:2:2 type formed with 10-bit word sequences or the HD signal formed with 12-bit word sequences has been standardized in accordance with SMPTE 292M or SMPTE 372M established by the SMPTE as mentioned above, the serial transmission of the D-Cinema signal for which any forbidden code is not predetermined has not been subjected yet to the standardization by the SMPTE.
Then, it is likely to propose to cause, for example, a D-Cinema signal of the 4:4:4 type formed with 12-bit word sequences to be subjected to serial transmission in accordance with Dual Link 292M Interface provided by SMPTE 372M in the same manner as the serial transmission of the HD signal formed with 12-bit word sequences. In such a case, the D-Cinema signal of the 4:4:4 type formed with 12-bit word sequences may be converted into, for example, bit sequence data of two channels each having a data rate (bit rate) of 1.485/1.000 Gb/s or 1.485/1.001 Gb/s and then transmitted through a data transmission path. If this proposal is possible, the serial transmission of the D-Cinema signal of the 4:4:4 type formed with 12-bit word sequences can be realized with use of circuit elements having been developed for the serial transmission in accordance with Dual Link 292M Interface provided by SMPTE 372M.
However, the serial transmission in accordance with Dual Link 292M Interface provided by SMPTE 372M has been provided for the HD signal in which each portion corresponding to a video data period does not contain any forbidden code. Therefore, if the serial transmission in accordance with Dual Link 292M Interface provided by SMPTE 372M is applied to the D-Cinema signal in which some forbidden codes may appear in a portion corresponding to each video data period, such a trouble in data transmission that the original D-Cinema signal can not be appropriately reproduced from the transmitted digital data based on the D-Cinema signal in a data receiving side where the transmitted digital data are received is likely to occur when the forbidden code appears actually in the portion of the D-Cinema signal corresponding to the video data period.
Under such a situation, it is desired that a data transmitting system by which the serial transmission-of the D-Cinema signal of the 4:4:4 type formed with, for example, 12-bit word sequences is realized without troubles resulting from the fact that any forbidden code is not predetermined for the D-Cinema signal so as not to eliminate the forbidden code from a portion of the D-Cinema signal corresponding to each video data period. However, for the present, any practical embodiment of data transmitting system which can realize appropriately the above-mentioned serial transmission of the D-Cinema signal has not been previously found. Further, any literature, paper or thesis disclosing practical technology related to the data transmitting system which can realize appropriately the above-mentioned serial transmission of the D-Cinema signal has not been previously found also.